1. Field of the Invention
The present invention relates to a common control redundancy switch method, and more particularly to a common control redundancy switch method capable of, when an error occurs at an active common control unit for managing and controlling a network of a very small aperture terminal system (VSAT), replacing the card at which the error occurs by a spare card, thereby allowing the common control unit to operate as usual.
2. Description of the Prior Art
Referring to FIG. 1, there is illustrated a common control device used to accomplish a conventional common control redundancy switch method. As shown in FIG. 1, the common control device includes a first common control unit 1 and a second common control unit 2 both adapted to manage and control a network of a VSAT. A first monitor processing unit 3 and a second monitor processing unit 4 are also provided. The first monitor processing unit 3 serves to exchange information with a network management system (NMS) and the common control unit 1, serves as an interface of a monitoring processor bus, and serves to achieve a communication of a bit synchronous card (BS) through the monitoring processor bus by utilizing a direct memory access (DMA) system. In similar to the first monitor processing unit 3, the second monitor processing unit 4 serves to exchange information with a network management system (NMS) and the common control unit 2, serves as an interface of the monitoring processor bus, and achieve a communication of the BS through the monitoring processor bus by utilizing the DMA system. The common control device further includes a performance monitor 5 serving as a switch for connecting the currently active one of the common control units 1 and 2 with the bus of the corresponding one of the monitor processing units 3 and 4 so as to achieve a common control redundancy switching operation, a maintenance read-out (MRO) monitor 6 as a monitor for displaying a debug message, and a call record journal (CRJ) monitor 7.
Each of the first and second common control units 1 and 2 includes a card for performing the whole control functions to down-load and store data base and protocol predetermined on a shelf and structured in the NMS, perform initiations of all boards of a district center and end offices, and monitor operating conditions. In each of the first and second common control units 1 and 2, a kernel of a multi-tasking operating system (MTOS) which is a commercial operating system and a software of the common control unit are operated. Each of the first and second common control units 1 and 2 also includes a paged memory pool of total pages of 2 mega bytes so as to manage the protocol software and database down-loaded from the NMS.
In the common control device having the above-mentioned arrangement, however, the overall system can not operate when an error occurs at a part thereof.
For solving such a problem that the overall system or circuit operates normally no longer due to a failure generated at a part thereof, there has been made a proposal of providing a redundant system or circuit to be switched for the failed system or, thereby enabling the overall system or circuit to continuously perform its normal operation. For example, such a proposal is disclosed in U.S. Pat. No. 5,196,734. In accordance with this patent, a cascode current switch latch is provided which is made insensitive to single event upset (SEU) from radiation-induced charge by the addition of two transistors connected thereto, thereby achieving a switching operation. However, this technique is adapted to solve the problems encountered in the field of integrated circuits due to a decrease in transistor size. The technique can not be applied to VSATs driven by digital signals.